When no one else is listening you might be tempted to throw in a 'honeybun' or something similar. When you're 65, dear seems to be the term of choice.
Read and be scared. Very scared...
And probably, somewhere along the way, you're going to want to refer to your SO as something other than SO.
When you're 16, boyfriend/girlfriend sounds pretty good. When you're wanting to strike a business deal, partner probably fits the bill. Lover just sounds like you're about to describe a bodily function.